Session Initiation Protocol (SIP) is an application-layer signaling protocol for creating, modifying, and terminating communication sessions with one or more participants. SIP operates independently from an underlying transport layer, and thus can be used with a variety of transport protocols. As such, SIP has gained wide acceptance in recent years and now is commonly used in a variety of communication systems, including those that support mobile communications.
In a typical mobile communication scenario, for example when a mobile communication device (mobile device) is moving while being used, the mobile device may roam from an area serviced by a first communication network (first network) that is SIP based to an area serviced by a second communication network (second network) that is also SIP based or is circuit-switched (CS). When this occurs during a call, a new communication segment needs to be established in the second network before the original communication segment with the first network is released.
The release of the original communication segment is typically initiated by communicating a notification to the mobile device via the first network to indicate to the mobile device that the original communication segment is being released. Unfortunately, if the mobile device loses connectivity to the first network before receiving such notification, the mobile device cannot immediately release the original communication segment in a conventional manner. An attempt to do so may be interpreted by the communication network as a release of the communication session.